Transformation of continuous alternating voltage (e.g., sinusoidal voltage) is typically carried out by utilizing closed circuit magnetic core transformers and electrical inductive (e.g., coils) elements. These transformation techniques suffers from the large weight and size of the transformers (typically up to 10 kG per one kW of transformed power), and from the difficulties associated with starting the transformers (the initial current in the transformer's primary coil may exceed the operating current by a factor of 6 to 8). Other drawbacks of these transformation techniques are due to the absence of protection against short circuit currents and due to the difficulties in gradually changing their output voltage in a continuous fashion.
According to another conventional voltage transformation scheme High Frequency (HF) transformers are utilized, the weight of which is typically in the range of 1.5 to 2 kG per 1 kW of transformed power. However, the transformation methods realized utilizing these transformers are complex due to the necessity to rectify and regulate the alternating current, and due to the filtering stages, required to assure that at any given time the converted voltage does not exceeds the required voltage. In addition, these transformation techniques often requires sophisticated control means for adjusting the shape of the output voltage to correspond to the shape of the input power source. Moreover, in these transformation techniques the voltage of the alternating power source is usually modulated by a HF rectangular or stepped pulse signal, which narrows the scope of applications that can employ these techniques, since most AC electrical appliances cannot effectively function when powered by a non-sinusoidal voltage.
Heretofore power conversion schemes were mainly based on PWM (Pulse Width Modulation) techniques wherein the power delivered to a load is controlled by a switching device being toggled between its open (disconnect—“OFF”) and close (connect—“ON”) states, wherein the delivered power is determined by the ratio between the time periods of the OFF and ON states of the switching device. These conversion schemes are efficient in terms of power efficiency, however, they suffer from various disadvantages such as emission of undesirable electromagnetic radiation and distortions in the converted signal due to presence of noises and redundant harmonies.
U.S. Pat. No. 6,346,778 (to Murray Mason et al.,) describes an AC (Alternating Current) power converter capable of adapting its output to capacitive, inductive, and/or resistive loads by utilizing a switching device the operation of which is controlled by a controller that regulates the power delivered to the output load according to the voltage and current inputs and their phase differences, which allows dissipating residual energy in the power converter.
U.S. Pat. No. 6,784,708 (to Rainer Krenzke) describe a high voltage output driver for a variable voltage range based on slew rate sensing. This driver comprises a slope transformer, a differentiator, a regulator, comparator, and a digital regulator which are connected together in a closed loop. While this converter is capable of providing stabilized adjustable output voltages, it is complex and costly.
The methods described above have not yet provided satisfactory solutions to the problems of the prior art. Therefore there is a need for an efficient and simplified transforming and regulating device that overcomes the above mentioned problems.
It is therefore an object of the present invention to provide an efficient adjustable and relatively lightweight transforming and regulating device capable of providing stabilized adjustable output voltages that does not require filtering stages and that does not introduce interferences in the electricity network.
It is another object of the present invention to provide an efficient adjustable and relatively lightweight transforming and regulating device having “soft start” capabilities.
It is a further object of the present invention to provide an efficient adjustable and relatively lightweight transforming and regulating device which is not based on Pulse Width Modulation (PWM) techniques.
It is yet another object of the present invention to provide a method and device for efficiently converting alternating voltage signals via a HF transformer by adjusting the voltages over the transformer coils by using one or more High Frequency Electromagnetic Voltage Regulator (HFEVR).
It is a further object of the present invention to provide a regulated transformation device wherein the transformation process can be controlled by HFEVR(s).
It is still another object of the present invention to provide a HFEVR with adjustable reactive resistance.
An additional object of the present invention is to provide a regulated transformer which provides control capabilities over the amplitudes and waveforms of the transformed signals.
Other objects and advantages of the invention will become apparent as the description proceeds.